1. Field of the Invention
The present invention relates to a fluid-filled vibration isolator and, more particularly, to a fluid-filled vibration isolator having excellent durability which is manufactured at low cost.
2. Description of Related Art
A fluid-filled vibration isolator generally includes two fluid chambers separated by a partition interconnected by a throttle passage provided in the partition. Upon input of vibration, walls defining the fluid chambers deform thus forcing a working fluid through the throttle passage and thereby damping the input vibration.
In order to reduce the weight of the above-described fluid-filled vibration isolator, it has been proposed to compose the partition and throttle passage of a pair of superimposed thin plates. One example of such a fluid-filled vibration isolator is disclosed in Japanese Patent application laid-open No. Hei 2-292539 and is illustrated in FIG. 5.
As shown, a mounting member 12 is embedded centrally in a hollow, thick-walled, rubber body 10 forming an engine mount. An annular side plate 16 is bonded to an outer surface of the rubber body 10 at its radially enlarged upper part. A lower part 14 of the annular side plate 16 extends vertically below the upper part. A lower end edge 18 of the side plate 16 first bends horizontally and outwardly and then bends vertically and downwardly into a generally C-shaped cross-section. The lower end edge 18 is secured to a peripheral edge of a bottom plate 20 by caulking. A mounting bolt 22 penetrates an axial center of the bottom plate 20.
Peripheral edges of both a partition 24 and a rubber diaphragm 26 are joined and sandwiched strongly by the lower end edge 18. A working fluid is sealed within a closed space defined by the rubber body 10 and the rubber diaphragm 26 such that a main fluid chamber 28 and an auxiliary fluid chamber 30 are formed by the partition 24.
The partition 24 is composed of two thin plates 32 and 34. The peripheral edges of the two thin plates 32 and 34 first bend downwardly and then horizontally. The horizontal edge portions are secured with the rubber diaphragm 26 by the lower and edge 18. The vertical peripheral edges of the two plates 32 and 34 define a closed annular space S. The closed annular space S opens into the main fluid chamber 28 and the auxiliary fluid chamber 30 thereby forming a throttle passage.
This isolator, however, requires troublesome press-forming, positioning and welding of the two thin plates 32 and 34 which increases manufacturing costs.
Another example of a lightweight, fluid-filled vibration isolator is disclosed in Japanese Utility Model application laid-open No. Hei4-39444, and is illustrated in FIG. 6. As shown, a partition 24 is composed of a single thin plate providing simple construction of the device and reduced weight. The partition 24 folds and further bends into an L-shaped cross-section. The folding part 36 abuts an inner surface of the rubber body 10, and the peripheral edge of the partition 24 is secured by the lower end edge 18. The inner surface of the side plate 14 and the L-shaped part of the partition 24 define a closed annular space S having a triangular cross-section. The closed annular space S opens into the main fluid chamber 28 and the auxiliary fluid chamber 30 thereby forming a throttle passage.
This isolator, however, cannot be formed easily because the folding part 36 must be deep drawn which increases the manufacturing costs.
Furthermore, in each example, the lower part of the side plate 14 bends at right angles, as shown by arrow A in FIG. 5, which causes stress concentrations in a single corner of the side plate 14 upon vibration, and accordingly, the durability of the device is decreased.